Engineering: What's soil got to do with it? Clay Robinson, PhD, CPSS, PG crobinson@wtamu.edu, http://www.wtamu.edu/~crobinson, copyright 2009 Merriam-Webster Online Dictionary soil, noun 1 : firm land : EARTH 2 a : the upper layer of earth that may be dug or plowed and in which plants grow b : the superficial unconsolidated and usually weathered part of the mantle of a planet and especially of the earth 3 : COUNTRY, LAND <our native soil> 4 : the agricultural life or calling 5 : a medium in which something takes hold and develops Spangler & Handy, 1982, Soil Engineering, Soils are natural materials which occur in infinite variety over the earth and whose engineering properties may vary widely from place to place within the relatively small confines of a single engineering project The properties of soils are continuously changing as the amount of moisture fluctuates and other environmental influences vary and may change dramatically under load Soil is used as construction material Perspectives Soil Physics - Soil is a dynamic, heterogeneous, three-phase, porous media Botany, Agronomy, Horticulture - Soil is the outer layer of the earth s crust capable of supporting plant growth (Pearson, 1967, Principles of Agronomy) Geology, Engineers - Soil is unconsolidated, surficial material. Engineering uses of soil: building media, foundation material,... Retaining Walls: The Good, The Bad, and the Ugly http://www.wtamu.edu/~crobinson/drdirt/retainingwalls.pdf SWPPP - Storm Water Pollution Prevention Plan http://www.wtamu.edu/~crobinson/drdirt/sw3p.pdf http://www.wtamu.edu/~crobinson/drdirt/erosoinrunoff.pdf Texture, Density: Sieves, cores, core caps texture classification systems (USDA triangle and Unified and AASHTO systems follow) Activities: swelling soils, packing for maximum density Sand, gravel, soil, silica flour, bentonite, water: wet bulk density vs dry bulk density Well sorted vs. well graded: Example Limitations for using soil for buildings and rural uses, e.g., houses with basements, septic tank absorption fields, local roads and streets, etc. Excerpt from Collegiate Soils Contest Guidelines: Profile description, site characteristics, soil classification, interpretations http://www.wtamu.edu/~crobinson/drdirt/regivexcerpt.pdf WebSoilSurvey http://websoilsurvey.nrcs.usda.gov Texas Panhandle Soils and Palo Duro Canyon introduction http://www.wtamu.edu/~crobinson/drdirt/txpnhndlsoils.pdf
AASHTO - American Association of State Highway and Transportation Officials http://training.ce.washington.edu/wsdot/modules/04_design_parameters/aashto_terms.htm AASHTO soil terminology comes from AASHTO M 145, Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes. Aggregate terminology comes from AASHTO M 147, Materials for Aggregate and Soil-Aggregate Subbase, Base and Surface Courses. Basic terms include: Boulders & Cobbles Material retained on a 75-mm (3-inch) Gravel Material passing a 75-mm (3-inch) sieve and retained on a 2.00-mm (No. 10) Coarse Sand Fine Sand Silt-Clay Silt Fraction Clay Fraction Silty Clayey Coarse Aggregate Fine Aggregate Material passing a 2.00-mm sieve (No. 10) and retained on a 0.475-mm (No. 40) Material passing a 0.475-mm (No. 40) sieve and retained on a 0.075-mm (No. 200) Material passing a 0.075-mm (No. 200) Material passing the 0.075 mm and larger than 0.002 mm. Material smaller than 0.002 mm. Material passing a 0.075-mm (No. 200) sieve with a PI#10 Material passing a 0.075-mm (No. 200) sieve with a PI$11 Aggregate retained on the 2.00 mm sieve and consisting of hard, durable particles or fragments of stone, gravel or slag. A wear requirement (AASHTO T 96) is normally required. Aggregate passing the 2.00 mm (No. 10) sieve and consisting of natural or crushed sand, and fine material particles passing the 0.075 mm (No. 200) The fraction passing the 0.075 mm (No. 200) sieve shall not be greater than two-thirds of the fraction passing the 0.425 mm (No. 40) The portion passing the 0.425 mm (No. 40) sieve shall have a LL # 25 and a PI # 6. Fine aggregate shall be free from vegetable matter and lumps or balls of clay. Note that these definitions are AASHTO definitions and are slightly different than those of the Unified Soil Classification system (ASTM). The table below shows the AASHTO soil classification system (from AASHTO M 145).
AASHTO Soil Classification System (from AASHTO M 145 or ASTM D3282) General Classification Granular Materials 35% or less passing the 0.075 mm sieve Silt-Clay Materials >35% passing the 0.075 mm sieve Group Classification A-1 A-3 A-2 A-4 A-5 A-6 A-7 Sieve Analysis, % passing A-1-a A-1-b A-2-4 A-2-5 A-2-6 A-2-7 A-7-5 A-7-6 2.00 mm (No. 10) 50 max 0.425 (No. 40) 30 max 50 max 51 min 0.075 (No. 200) 15 max 25 max 10 max 35 max 35 max 35 max 35 max 36 min 36 min 36 min 36 min Characteristics of fraction passing 0.425 mm (No. 40) Liquid Limit 40 max 41 min 40 max 41 min 40 max 41 min 40 max 41 min Plasticity Index 6 max N.P. 10 max 10 max 11 min 11 min 10 max 10 max 11 min 11 min Usual types of significant constituent materials stone fragments, gravel and sand fine sand silty or clayey gravel and sand silty soils clayey soils General rating as a subgrade excellent to good fair to poor Plasticity index of A-7-5 subgroup is equal to or less than the LL - 30. Plasticity index of A-7-6 subgroup is greater than LL - 30 References: Day, Robert W. 2001. Soil testing manual: procedures, classification data, and sampling practices. McGraw-Hill Professional. ISBN 0071363637, 9780071363631 http://training.ce.washington.edu/wsdot/modules/04_design_parameters/aashto_terms.htm
ASTM (American Society for Testing and Materials) Terminology The Unified Soil Classification System is a soil classification system used in engineering and geology disciplines to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials. The basic reference for the Unified Soil Classification System is ASTM D 2487. Terms include: Coarse-Grained Soils More than 50 percent retained on a 0.075 mm (No. 200) sieve Fine-Grained Soils 50 percent or more passes a 0.075 mm (No. 200) sieve Gravel Material passing a 75-mm (3-inch) sieve and retained on a 4.75-mm (No. 4) Coarse Gravel Material passing a 75-mm (3-inch) sieve and retained on a 19.0-mm (3/4-inch) Fine Gravel Material passing a 19.0-mm (3/4-inch) sieve and retained on a 4.75-mm (No. 4) Sand Material passing a 4.75-mm sieve (No. 4) and retained on a 0.075-mm (No. 200) Coarse Sand Material passing a 4.75-mm sieve (No. 4) and retained on a 2.00-mm (No. 10) Medium Sand Fine Sand Clay Silt Peat Material passing a 2.00-mm sieve (No. 10) and retained on a 0.475-mm (No. 40) Material passing a 0.475-mm (No. 40) sieve and retained on a 0.075-mm (No. 200) Material passing a 0.075-mm (No. 200) that exhibits plasticity, and strength when dry (PI ³ 4). Material passing a 0.075-mm (No. 200) that is non-plastic, and has little strength when dry (PI < 4). Soil of vegetable matter. Each Group in the Unified Soil Classification System and is represented by a two-letter symbol. Prefix Suffix Letter Definition Letter Definition G gravel P poorly graded (uniform particle sizes) S sand W well graded (diversified particle sizes) M silt H high plasticity, LL > 50% C clay L low plasticity, LL < 50% O organic Unified Soil Classification (USC) System (from ASTM D 2487)
Major Divisions Group Symbol Typical Names Course-Grained Soils More than 50% retained on the 0.075 mm (No. 200) sieve Gravels 50% or more of course fraction retained on the 4.75 mm (No. 4) sieve Sands 50% or more of course fraction passes the 4.75 (No. 4) sieve Clean Gravels GW Well-graded gravels and gravel-sand mixtures, little or no fines Gravels with Fines GP GM GC Poorly graded gravels and gravel-sand mixtures, little or no fines Silty gravels, gravel-sand-silt mixtures Clayey gravels, gravel-sand-clay mixtures Clean Sands SW Well-graded sands and gravelly sands, little or no fines Sands with Fines SP SM SC Poorly graded sands and gravelly sands, little or no fines Silty sands, sand-silt mixtures Clayey sands, sand-clay mixtures Fine-Grained Soils More than 50% passes the 0.075 mm (No. 200) sieve Silts and Clays Liquid Limit 50% or less ML CL OL Inorganic silts, very fine sands, rock four, silty or clayey fine sands Inorganic clays of low to medium plasticity, gravelly/sandy/silty/lean clays Organic silts and organic silty clays of low plasticity Silts and Clays Liquid Limit greater than 50% MH CH Inorganic silts, micaceous or diatomaceous fine sands or silts, elastic silts Inorganic clays or high plasticity, fat clays OH Organic clays of medium to high plasticity Highly Organic Soils PT Peat, muck, and other highly organic soils Prefix: G = Gravel, S = Sand, M = Silt, C = Clay, O = Organic Suffix: W = Well Graded, P = Poorly Graded, M = Silty, L = Clay, LL < 50%, H = Clay, LL > 50%
USDA (United States Department of Agriculture) Particle size analysis Coarse fragments > 2 mm Stones or boulders >250 mm Cobbles (round) 250-75 mm Flags (flat) 250-75 mm Gravel 75-2 mm Coarse fragments are included as modifiers to the USDA soil texture class Soil separates Sand Very coarse Coarse Medium Fine Very fine Silt Clay 2.0-0.05 mm 2.0-1.0 mm 1.0-0.5 mm 0.5-0.25 mm 0.25-0.1 mm 0.1-0.05 mm 0.05-0.002 mm <0.002 mm (2 µm) Soil texture - the relative proportion of the particles < 2.0 mm. The different proportions of particle sizes are grouped in the USDA Soil Textural Triangle according to the way the soil properties affect agricultural management practices. USDA Texture Triangle 100 0 90 10 80 20 0 20 Clay Separate, % 30 40 50 10 loamy sand sand 100 90 80 60 70 sandy clay sandy clay loam sandy loam 70 60 clay clay loam loam 50 40 Sand Separate, % 30 40 silty clay 30 Silt Separate, % 50 silty clay loam silt loam 60 20 70 silt 10 80 90 0 100